Flame retardant adhesives for films

Abstract

A film includes an adhesive layer having an adhesive polymer and a polyphosphonate on a substrate layer, where the adhesive layer is optically clear and has low flammability.

Description

[0001] The present disclosure relates to adhesives for films, and particularly to flame retardant adhesives for films.

[0002] Adhesives have been used for a variety of marking, fastening, protecting, sealing, and masking applications. Adhesive tapes generally include a backing or substrate and an adhesive. One class of adhesives, namely pressure sensitive adhesives, is particularly useful for many applications.

[0003] Pressure sensitive adhesives are well known to those of ordinary skill in the art and have certain properties at room temperature including: (1) strong and persistent tack, (2) the ability to adhere by finger pressure, (3) sufficient ability to remain on the adherend, and (4) sufficient cohesive strength to cleanly remove from the adherend. Materials that have been found to work well as pressure sensitive adhesives are polymers that are designed and formulated to exhibit the desired viscoelastic properties such that the tack, peel adhesion, and shear strength are at a desired balance. The most commonly used polymers for preparing pressure sensitive adhesives are natural rubber, synthetic rubbers (e.g., styrene / butadiene copolymer (SBR) and styrene / isoprene / styrene (SIS) block copolymer), various (meth)acrylate (e.g., acrylate and methacrylate) copolymers, and silicones. Each of these types of materials has advantages and disadvantages. SUMMARY OF THE INVENTION

[0004] The present disclosure provides a film that can be optically clear and has low flammability.

[0005] In one aspect, the film includes a base layer and an adhesive layer on the base layer. The adhesive layer has an adhesive polymer and a polyphosphonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] To easily identify the discussion of any particular element or action, one or more of the most significant digits in the reference numerals refer to the drawing number in which the element was first introduced.

[0007] Figure 1 Aspects of the subject matter in accordance with one embodiment are illustrated. DETAILED DESCRIPTION

[0008] The use of adhesives, especially pressure-sensitive adhesives, is becoming increasingly widespread. Areas where the use of adhesives is growing include the medical, electronics, and optical industries, as well as consumer products and public transportation. These industries require adhesives to have special properties. For example, adhesives (such as pressure-sensitive adhesives) are required to have special properties superior to traditional tack, peel adhesion, and shear strength. To meet the increasingly demanding performance requirements for adhesives, various new materials are needed. Among the various performance requirements are optical clarity and flame retardancy. Optical clarity is usually required for adhesives because the adhesive layer is often a component of an optical article or device; and flame retardancy is required for adhesives to inhibit or slow the spread of fire to protect people and property. In various applications, such as for graphic films or overlaminate materials, some adhesives such as acrylic adhesives can have a significant impact on the overall flammability, especially when the mass of the adhesive relatively constitutes a significant percentage of the structure. Reducing the flammability of the adhesive can significantly reduce the flammability of the entire structure, especially in terms of combustion calorimetry.

[0009] The adhesives of the present disclosure can be used in films to provide flame retardancy, optical clarity, and adhesive properties in various applications. Applications can include applying a transparent adhesive layer to a substrate layer, and applying a structure to a substrate. Non-limiting examples of applications include for overlaminate films, surface protection films, window films, or other glass surface films. In some embodiments, the adhesive can be used to form an adhesive layer comprising an adhesive polymer and a polyphosphonate.

[0010] Figure 1 An example of a film 102 according to the present disclosure applied to a substrate 108 is shown. Film 102 includes a substrate layer 104 and an adhesive layer 106. The adhesive layer 106 can provide appropriate adhesive properties between the substrate layer 104 and the substrate 108 for a particular application. The substrate layer 104 can be a polymer film. Non-limiting examples of polymer films include polyester, vinyl, polyolefin, polyurethane, acrylic, polylactic acid, or combinations thereof, or multilayer films.

[0011] The various layers of film 102 can be selected based on the application and the type of substrate 108. Film 102 can be applied to various types of substrates 108. In some embodiments, the substrate 108 is a polymer or metal substrate. Non-limiting examples of polymer substrates include various types of laminated materials, such as polyester, vinyl, polyolefin, polyurethane, acrylic, polylactic acid, or combinations thereof. Non-limiting examples of metal substrates include aluminum.

[0012] Various forms of film 102 include tapes, multilayer films with additional layers (such as low-adhesion coatings), etc. Such applications can provide film 102 in the form of sheets or rolls.

[0013] In some embodiments, to provide suitable adhesion properties, the adhesive layer 106 may have a peel adhesion (force / length) of greater than or equal to 350 N / m, 525 N / m, 700 N / m, 875 N / m, 1050 N / m, 1225 N / m, 1400 N / m, 1575 N / m or even 1750 N / m, particularly when laminated to a polymer on a metal substrate. In some embodiments, the peel adhesion is less than or equal to 1925 N / m, 1750 N / m, 1575 N / m, 1400 N / m, 1225 N / m, 1050 N / m, 875 N / m, 700 N / m or even 525 N / m. The peel adhesion is defined using the measurement results from a peel adhesion test method and can be applied to various time ranges and conditions, including 24 hours at ambient temperature and humidity (23 °C and 50% relative humidity), 7 days at ambient temperature and humidity or 7 days at 65 °C. In many applications, a peel adhesion of greater than or equal to 350 or 525 after 24 hours at ambient temperature and humidity may be particularly desirable.

[0014] In some embodiments, when tested on a metal substrate (e.g., aluminum), the peel adhesion after 24 hours at ambient temperature and humidity is at least 1050 N / m, and the peel adhesion after 7 days at 65 °C is at least 700 N / m. In one or more embodiments, when tested on a metal substrate (e.g., aluminum), the peel adhesion after 24 hours at ambient temperature and humidity is at least 1400 N / m, and the peel adhesion after 7 days at 65 °C is at least 700 N / m.

[0015] In some embodiments, when tested on a polymer substrate (e.g., vinyl), the peel adhesion after 24 hours at ambient temperature and humidity is at least 700 N / m, and the peel adhesion after 7 days at 65 °C is at least 700 N / m. In one or more embodiments, when tested on a metal substrate (e.g., aluminum), the peel adhesion after 24 hours at ambient temperature and humidity is at least 700 N / m, and the peel adhesion after 7 days at 65 °C is at least 1050 N / m.

[0016] Generally, when laminated to a polymer or metal substrate, the peel adhesion of the adhesive layer 106 of the film 102 is greater than the peel adhesion of an adhesive layer 106 without polyphosphonate.

[0017] The base layer 104, the adhesive layer 106, or both can be optically transparent. As used herein, the term "optically clear" refers to high light transmittance over at least a portion of the visible light spectrum (from about 400 nm to about 700 nm) and exhibits low haze. Generally, an optically clear article has a visible light transmittance of at least 90%, 91%, 92%, 93%, 94%, or even 95%, and a haze of less than or equal to 5%, 3%, 2%, or even 1.5%. The haze is defined using the measurement results from the haze test method.

[0018] In some embodiments, the adhesive layer 106 has a transmittance of at least 93% and a haze of less than or equal to 2%. In one or more embodiments, the adhesive layer 106 has a transmittance of at least 94% and a haze of less than or equal to 1%.

[0019] The thickness of the adhesive layer 106 can be selected based on the desired haze. Appropriate thickness and haze can be selected by those skilled in the art benefiting from this disclosure based on the application.

[0020] The base layer 104, the adhesive layer 106, or both can be optically transparent. As used herein, the term "optically transparent" refers to high light transmittance over at least a portion of the visible light spectrum. Generally, an optically transparent article has a visible light transmittance of at least 80%. The term "transparent film" refers to a film having a certain thickness, and when the film is disposed on a substrate, an image (disposed on or adjacent to the substrate) is visible through the thickness of the transparent film. In many embodiments, the transparent film allows the image to be seen through the thickness of the film without significant loss of image clarity. In some embodiments, the film has a matte surface or a gloss surface. When the film 102 is transparent, both the base layer 104 and the adhesive layer 106 are transparent. In other embodiments, the base layer 104 can be opaque or have a light transmittance of less than 80%.

[0021] The base layer 104, the adhesive layer 106, or both can be colorless. As used herein, the term "colorless" refers to a color difference (ΔE or ΔE*) of less than 1 according to the color test method. In some embodiments, the base layer 104, the adhesive layer 106, or both have a ΔE* of less than or equal to 2, 1.5, 1, 0.75, or even 0.7. In some embodiments, the adhesive layer 106 has a ΔE* of less than or equal to 0.75. In other embodiments, the base layer 104 or the adhesive layer 106 can have a color or be described as colored (e.g., ΔE* greater than 2).

[0022] The adhesive layer 106 includes at least an adhesive polymer and a polyphosphonate as a flame retardant additive. The adhesive polymer can be selected to be suitable for a pressure-sensitive adhesive or a hot-melt adhesive. In some embodiments, the adhesive polymer includes one or more acrylates for a pressure-sensitive adhesive, such as 2-ethylhexyl acrylate (2-EHA). In particular, the adhesive polymer can include a polymer chain formed by reacting one or more acrylates.

[0023] The polymer chain can be formed by reacting at least two different types of acrylates in an amount between 90% and 92.5% by weight of the adhesive polymer. The polyphosphonate can be added after such reaction. In some embodiments, the reaction includes at least one acrylate having an alkyl ester group with a longest carbon chain length less than or equal to 4. The reaction can include methyl acrylate (MA), butyl acrylate (BA), or both. In some embodiments, the reaction includes 2-ethylhexyl acrylate (2-EHA) in an amount between 45% and 70% by weight of the adhesive polymer (the total weight of the monomers in the adhesive polymer does not include any solvent). In some embodiments, the reaction includes acrylic acid (AA) in an amount greater than or equal to 7.5%, or even 8.75% by weight of the adhesive polymer. AA can be included in an amount of up to 10% by weight of the adhesive polymer.

[0024] The halogen-free polyphosphonate can be included in the adhesive layer in various suitable amounts. In some embodiments, based on the weight of the adhesive layer (the total weight of the adhesive layer after drying or curing, where the total weight of the adhesive layer is the sum of the weights of the adhesive polymer and the polyphosphonate), the polyphosphonate is greater than or equal to 5%, 10%, 15%, or even 20%. Based on the weight of the adhesive layer, the polyphosphonate can be less than or equal to 30%, 25%, or even 20%. In particular, based on the weight of the adhesive layer, the polyphosphonate can be between 10% and 20%.

[0025] The polyphosphonate can include an oligomer having a molecular weight (MW) greater than 7500, 8000, or even 8500. The MW can be less than or equal to 10000, 9500, or even 9000. The polydispersity index (PI) of the polyphosphonate can be less than 4, 3.5, 3, or even 2.75. The PI can be greater than or equal to 1.5, 2, or even 2.5. In some embodiments, the polyphosphonate is a non-cyclic polymer. In some embodiments, the polyphosphonate does not contain an alcohol functional group. Non-limiting examples of suitable polyphosphonates include the Nofia HM5000 flame retardant additive available from FRX Polymers, Inc., Chelmsford, MA.

[0026] Generally, the adhesive polymer and the polyphosphonate are selected to be compatible to provide an optically clear adhesive layer 106 with low flammability, particularly in terms of combustion calorimetry measured by the micro combustion calorimetry test method. Generally, to provide sufficient flame retardancy, the adhesive layer 106 has a sufficient amount of flame retardant additives selected by those skilled in the art who benefit from the present disclosure.

[0027] Compatibility can be indicated by the lack of a melting endotherm, particularly as measured by the differential scanning calorimetry test method. In some embodiments, the adhesive layer 106 particularly does not have a melting endotherm at temperatures above 373 K, or at temperatures between 100 °C and 150 °C. Generally, the lack of a melting endotherm can be associated with a low haze %. In some embodiments, the optically clear adhesive layer 106 can have polymer chains formed by reacting 2-EHA, MA, or BA with at least 8.75% AA by weight of the adhesive polymer and approximately 20% polyphosphonate as an additive.

[0028] The film 102 can be made in any suitable manner. Generally, the components of the adhesive polymer can react to form a solution comprising the adhesive polymer. The polyphosphonate can be added to the solution. Then, the solution can be coated onto the substrate layer 104, dried, and cured to form an adhesive layer 106 on the substrate layer 104. Then, the film 102 can be used in various applications.

[0029] Example

[0030] Flame retardant pressure sensitive adhesive compositions and adhesive-coated films were prepared and their material properties were characterized. These examples are for illustrative purposes only and are not intended to limit the scope of the appended claims. Unless otherwise indicated, all parts, percentages, ratios, etc. in the examples and the remainder of the specification are by weight. Unless otherwise indicated, the solvents and other reagents used were obtained from Sigma-Aldrich Chemical Company, St. Louis, Missouri. The following abbreviations are used herein: °C = degrees Celsius; h = hour; min = minute; kPa = kilopascal; N / m = Newton per meter; ΔE* = color difference; K / sec = Kelvin per second; J / g-K = joule per gram Kelvin; K = Kelvin; K = Kelvin; kJ / g = kilojoule per gram; mJ / cm 2 = millijoule per square centimeter.

[0031] Material List

[0032]

[0033] Haze Test Method

[0034] Haze, clarity, and transmittance were measured according to ASTM D 1003-13 using BYK Haze-Gard Plus model AT-4725 (obtainable from BYK-Gardner, Columbia, Md.). The adhesive was applied directly to the polyester film and measured.

[0035] Color Test Method

[0036] The color difference of the adhesive was measured according to ASTM D2244-16 using an X-RITE spectrophotometer model Ci62 (obtainable from X-Rite, Grand Rapids, MI) at a D65 / 100 illuminant / observer. The color shift or color difference (ΔE*) of the film-backed adhesive sample laminated to a white vinyl film (obtainable as 3M CONTROLTAC IJ180MC-10 from 3M, St. Paul, MN) was calculated from the measured CIELAB color space values with the neat adhesive as a reference according to the following equation:

[0037]

[0038] Peel Adhesion Test Method

[0039] Peel adhesion was measured according to ASTM D330-04 using an INSTRON model 5965 (obtainable from Instron, Norwood, MA). The film-backed adhesive sample was cut into 25.4 mm wide strips and then manually applied with a spatula to a Q-Panel aluminum plate (obtainable as 6061T6 SP-104177 from Q-Lab, Westlake, OH) or an aluminum plate covered with a vinyl film (obtainable as 3M CONTROLTAC IJ180MC-10 from 3M, St. Paul, MN). The samples were conditioned for a specified dwell time in a constant temperature and humidity (23 °C and 50% relative humidity) or an oven set at 65 °C. After the specified conditioning, the peel adhesion was measured by peeling the sample from the substrate at a 180-degree angle at a removal rate of 30.5 cm / min. The peel adhesion was measured in pounds force per inch (lbf / in) and converted to newtons per meter (N / m).

[0040] Micro Combustion Calorimetry (MCC) Test Method

[0041] The flammability of the binder was measured using a microscale combustion calorimeter model MCC-2 (obtainable from Govmark, Farmingdale, NY) according to Method A of ASTM D7309-13. A 2 mg to 3 mg cured binder sample was heated at a rate of 1 K / second in a nitrogen environment. The decomposition products were completely oxidized in a combustion chamber maintained at 900 °C with an environment of 20% oxygen and 80% nitrogen. The heat release of the decomposition gases was determined by the mass of oxygen used to completely combust the sample. The following parameters were calculated from the data:

[0042] Heat release capacity (J / g-K), which is the maximum specific heat release rate divided by the heating rate.

[0043] Specific heat release hc (kJ / g), which is the net heat release over the entire temperature range.

[0044] Pyrolysis residue Yp (%), which is the mass fraction of the sample remaining after testing.

[0045] Differential Scanning Calorimetry (DSC) Test Method

[0046] The thermal properties of the binder were measured using a differential scanning calorimeter DSC2500 Discovery series from TA Instruments, New Castle, DE.

[0047] A 3 mg to 5 mg cured binder sample was removed from the release liner and placed directly into a cup and then into an autosampler. The sample was subjected to a heating profile from 193 K to 423 K at a linear heating rate of 3 K / min or 20 K / min in a nitrogen atmosphere.

[0048] The DSC trace obtained was analyzed for the presence of a melting endotherm, usually above 393 K, as an indication of the compatibility between the flame retardant additive and the polymer.

[0049] Example Preparation

[0050] Examples E1 - E3, E8 - E11

[0051] A polyphosphate flame retardant adhesive solution was prepared by mixing 2-EHA, BA, MA, and AA with AEBP [0.35 phr, 1.05 g, 50% solution in ethyl acetate], Vazo 67 initiator (0.15 phr, or 0.225 g), and Irganox 1010 (0.15 phr, 0.23 g) in a 1-L amber bottle according to the ratios in Table 1 by weight. Isopropyl alcohol and ethyl acetate were added such that the total monomer concentration target was 50% by mass (total monomer + solvent solution = ~300 g). The amber bottle was capped with a PTFE-lined lid, and the contents of the amber bottle were mixed well. The lid was removed, and the solution was degassed by bubbling a constant nitrogen stream (ca. 1 L / min) through the solution for two minutes. The amber bottle was sealed again with a PTFE-lined lid, and the bottle was placed in a Launder-Ometer TM (Model M228AA) obtained from Atlas Electric Devices Co., Chicago, Ill., containing a 60 °C water bath for 20 to 24 hours. Then, an FR additive was added by weight percentage, and the solution was diluted with ethyl acetate to 47.6% ± 0.5% solids. The solution was coated onto the LI with a doctor blade coater at a 203-μm gap and dried in an oven set at 65 °C for 10 minutes. The dried coating was then cured with 60 mJ / cm2 of UVC light in a nitrogen stream through a Honle JetCURE UV curing unit (obtained from Honle UV America, Inc., Marlboro, MA). At a nip pressure of 276 kPa, the cured adhesive-coated release liner was laminated onto the film substrate at a speed of 0.9 to 1.5 m per minute using a laminator.

[0052] Table 1. Polyphosphonate Flame Retardant Adhesive Examples

[0053]

[0054]

[0055] Comparative Examples C0 - C11 (without flame retardant additives)

[0056] A comparative adhesive solution without a flame retardant binder was prepared by mixing 2-EHA, BA, MA, and AA with AEBP [0.35 phr, 1.05 g, 50% solution in ethyl acetate], Vazo 67 initiator (0.15 phr, or 0.225 g), and Irganox 1010 (0.15 phr, 0.23 g) in a 1 L amber bottle according to the ratios in Table 2 by weight. Isopropyl alcohol and ethyl acetate were added such that the total monomer concentration target was 50% by mass (total monomer + solvent solution = approximately 300 g). The amber bottle was capped with a PTFE-lined lid, and the contents of the amber bottle were mixed well. The lid was removed, and the solution was degassed by bubbling a constant nitrogen stream (approximately 1 L / min) through the solution for two minutes. The amber bottle was sealed again with a PTFE-lined lid and placed in a Launder-Ometer TM (Model M228AA) obtained from Atlas Electric Devices Co., Chicago, Ill., containing a 60 °C water bath, for 20 to 24 hours. Then, an FR additive was added by weight percentage, and the solution was diluted with ethyl acetate to 47.6% ± 0.5% solids. Comparative Example C0 was a 3 mil PET film without an adhesive coating. The solution was similarly coated and laminated onto a film substrate as described in Examples E1-E3, E8-E12.

[0057] Table 2. Comparative Examples of Non - Flame Retardant Adhesives

[0058]

[0059] Comparative Examples C14 - C17 (with flame retardant additives)

[0060] A polyphosphate flame retardant binder solution was prepared by mixing 2-EHA, BA, MA, and AA with AEBP [0.35 phr, 1.05 g, 50% solution in ethyl acetate], Vazo 67 initiator [0.15 phr, or 0.225 g], and Irganox 1010 [0.15 phr, 0.23 g] by weight in a 1-L amber bottle according to the ratios in Table 3. Isopropyl alcohol and ethyl acetate were added such that the total monomer concentration was targeted at 50% by mass (total monomer + solvent solution = ~300 g). The amber bottle was capped with a PTFE-lined cap, and the contents of the amber bottle were mixed well. The cap was removed, and the solution was degassed by bubbling a constant nitrogen stream (~1 L / min) through the solution for two minutes. The amber bottle was sealed again with a PTFE-lined cap and placed in a Launder-Ometer TM (Model M228AA) obtained from Atlas Electric Devices Co., Chicago, Ill., containing a 60 °C water bath, for 20 to 24 hours. Then, FR additives were added by weight percentage, and the solution was diluted to 47.6% ± 0.5% solids with ethyl acetate. The solution was similarly coated and laminated onto a film substrate as described in Examples E1-E3, E8-E12.

[0061] Table 3. Polyphosphonate Flame Retardant Adhesive Comparative Examples

[0062] Example Number 2 - EHA BA MA AA FR Additive Substrate C14 92.5 0 0 7.5 FRA (20%) F1 C15 46.2 46.2 0 7.5 FRA (20%) F1 C16 91.8 0 0 8.75 FRA (20%) F1 C17 90 0 0 10 FRA (20%) F1

[0063] Results

[0064] The examples were tested using the test methods listed above. The results are shown in Tables 4 to 7.

[0065] Table 4. Optical Transmittance, Haze, Clarity and Color Shift Results

[0066]

[0067]

[0068] Table 5. Micro Combustion Calorimetry (MCC) Results

[0069] Example HRC (ηc (J / g - K)) Residue (Yp (%)) Specific Heat Release (hc (kJ / g)) C1 591 0.8 32.0 C2 521 3.5 32.3 C3 559 1.5 32.0 E1 525 1.0 36.5 E2 458 1.4 32.4 E3 471 5.2 32.3 C4 606 1.2 36.4 C5 540 0.9 32.0 C8 565 2.1 33.0 C14 464 3.4 33.9 C15 457 5.6 30.8 E8 445 7.9 31.0 C6 555 1.2 34.1 C9 515 2.5 32.1 C10 519 0.4 31.4 C16 425 4.9 32.2 E9 432 5.3 30.3 E10 423 5.0 30.0 C7 547 1.2 33.9 C11 523 1.0 32.9 C17 421 3.7 31.8 E11 425 5.6 30.3

[0070] Table 6. Peel Adhesion Results

[0071]

[0072] *(23 °C and 50% relative humidity); NA indicates that the sample was not easily testable

[0073] Table 7. DSC Results

[0074]

[0075]

[0076] Accordingly, various embodiments of a flame retardant adhesive for a membrane are disclosed. Other features and combinations of features within the scope of the present disclosure may be apparent to those skilled in the art who benefit from the drawings, detailed description, and claims.

[0077] Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term "exactly" or "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein or, for example, within the typical ranges of experimental error.

[0078] Numerical ranges expressed using endpoint values include all numbers within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range.

[0079] The singular forms "a", "an", and "the" encompass embodiments having a plurality of referents, unless the context clearly indicates otherwise.

[0080] The phrases "at least one of...", "comprising at least one of...", and "one or more of..." followed by a list refer to any item in the list and any combination of two or more items in the list.

Claims

1. A film, comprising: A base layer; And An adhesive layer on the base layer, the adhesive layer comprising an adhesive polymer and a polyphosphonate.

2. The film according to claim 1, wherein the adhesive layer has a haze% of less than or equal to 3%.

3. The film according to claim 1 or 2, wherein when laminated to a polymer or metal substrate, the adhesive layer has a peel adhesion of greater than or equal to 350 N / m.

4. The film according to claim 3, wherein when laminated to a polymer or metal substrate, the peel adhesion of the adhesive layer is greater than that of an adhesive layer comprising the adhesive polymer without the polyphosphonate.

5. The film according to any one of claims 1 to 4, wherein the polymer or metal substrate has a vinyl or aluminum surface.

6. The film according to any one of claims 1 to 5, wherein the adhesive polymer comprises a polymer chain formed by reacting one or more acrylates.

7. The film according to claim 6, wherein the polymer chain is formed by reacting at least two different types of acrylates having a total amount between 90% and 92.5% by weight of the adhesive polymer.

8. The film according to claim 6 or 7, wherein the polymer chain is formed by reacting at least one acrylate having an alkyl ester group with a longest carbon chain length of less than or equal to 4.

9. The film according to any one of claims 6 to 8, wherein the polymer chain is formed by reacting methyl acrylate, butyl acrylate or both.

10. The film according to any one of claims 6 to 9, wherein the polymer chain is formed by reacting 2-ethylhexyl acrylate in an amount between 45% and 70% by weight of the adhesive polymer.

11. The film according to any one of claims 6 to 10, wherein the polymer chain is formed by reacting acrylic acid in an amount greater than or equal to 7.5% by weight of the adhesive polymer.

12. The film according to any one of claims 1 to 11, wherein the polyphosphonate comprises an oligomer having a molecular weight greater than 7000 and a polydispersity index less than 4.

13. The film according to any one of claims 1 to 12, wherein the polyphosphonate is a non-cyclic polymer.

14. The film according to any one of claims 1 to 13, wherein the polyphosphonate does not contain an alcohol functional group.

15. The film according to any one of claims 1 to 14, wherein the adhesive layer does not have an endothermic melting at a temperature higher than 393 K.

16. The film according to any one of claims 1 to 15, wherein the base layer is transparent.

17. The film according to any one of claims 1 to 16, wherein the adhesive layer is colorless.

18. The film according to any one of claims 1 to 16, wherein the polyphosphonate is 10% to 20% by weight of the adhesive layer.

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